The present invention relates to a large current control semiconductor device used in high temperature environments represented by use in automobiles. In particular, the present invention relates to a power semiconductor module that is excellent in heat resistance of its junction and constituent materials and excellent in thermal fatigue life against the thermal cycling test or the power cycling test caused by the on/off of the device, even in the case where operation is conducted with the junction temperature of the semiconductor device in the range of 175 to 250° C.
Power semiconductor modules including power devices, such as MOSFETs and IGBTs, for exercising switching control on a large current and diodes for releasing the reverse voltage generated at the time of switching are used in wide fields ranging from household electric appliances to vehicles as main components of inverter apparatuses for power converter. In recent years, motor control in the automobile field is promoted rapidly. As a result, the environment in which the power semiconductor module serving as its current control device is used becomes severe. For example, the power semiconductor module is installed in a place in a high temperature atmosphere where cooling cannot be conducted sufficiently, or the controlled current capacity tends to increase. As the performance of the power semiconductor module, therefore, high reliability that normal operation can be ensured in a use environment having a large temperature change over a long period and a high heat resistance capable of withstanding a high temperature caused in the device by an increase of heat generated by elements when a large current flows are demanded.
A structure known as a conventional power semiconductor structure is obtained by joining a conductor plate onto an insulating substrate with, for example, solder, joining a Ni/Au-plated back electrode of a power device to the conductor plate with Pb-free solder, joining a conductor lead for main electrode to a main electrode on a circuit face with an Al or Au bump, connecting a conductor lead for control electrode to a control electrode with an Al or Au wire, and sealing the power semiconductor module with a mold resin obtained by filling an epoxy resin with a silica filling material by means of the transfer mold method, in a state in which a bottom face of the insulating plate is exposed (JP-A-2004-247383). Cooling of the power semiconductor module is conducted by a cooling substance disposed under the insulating substrate.
Another known structure is obtained by providing a power device having a main electrode on one main face and having a main electrode and a control electrode on the other main face, providing two high thermal conductive insulating substrates so as to have the power device between and have electrode electrodes on sandwiching faces to join to the electrodes of the power device, joining the electrodes of the power device to the electrodes on the high thermal conductive insulating substrates with brazing, providing terminals for external wiring connection so as to extend to the outside in parallel to faces of the high thermal conductive insulating substrates, and filling a gap between the two high thermal conductive insulating substrates with an insulating resin (JP-A-10-56131). A structure obtained by providing convex parts on the high thermal conductive insulating substrates and joining tips of the convex parts to the other high thermal conductive insulating substrate is also disclosed. Cooling of the power semiconductor module is conducted by cooling substances disposed above and below the upper and lower high thermal conductive insulating substrates.